Method for operating an internal combustion engine

ABSTRACT

An operating method for an internal combustion engine is described, especially for a motor vehicle, in which, in a first operating mode, fuel is injected preferably for heating a catalytic converter and, in at least one further operating mode, into a combustion chamber. In order to prevent a sudden change in the torque produced by the internal combustion engine during the switchover from/to the first operating mode, a distribution factor influencing torque is taken into account in an actual branch and/or in a setpoint branch of controller of the internal combustion engine.

FIELD OF THE INVENTION

The present invention relates to a method for operating an internalcombustion engine, especially of a motor vehicle, in which, in a firstoperating mode, fuel is preferably injected for heating a catalyticconverter, and, in at least one further operating mode, into acombustion chamber, in which a controller controls/regulates theinternal combustion machine, and in which switching takes place betweenthe operating modes.

The present invention also relates to an internal combustion engine,especially for a motor vehicle, in which, in a first operating mode,fuel is able to be injected preferably for heating a catalytic converterand, in at least one further operating mode, into a combustion chamber,the internal combustion engine being able to be controlled/regulated bya controller, and switchable between the operating modes.

In addition, the present invention relates to a control unit for aninternal combustion engine, especially of a motor vehicle, in which, ina first operating mode, fuel is preferably able to be injected forheating a catalytic converter, and, in at least one further operatingmode, into a combustion chamber, the internal combustion engine beingable to be controlled/regulated by a controller, and in which switchingtakes place between the operating modes.

BACKGROUND INFORMATION

In direct fuel injection, fuel is injected into the combustion chamberof the internal combustion engine, in a homogeneous operation during theintake phase or in a stratified operation during the compression phrase.

An operating mode of the internal combustion engine briefly denoted as“HOSP” is also known, especially for the rapid heating up of a catalyticconverter, in which the fuel mass to be injected is divided up into twoindividual injections, of which the first takes place in the intakephase and the second in the compression phase of the internal combustionengine. The ratio of the injected fuel mass in the second injection tothe fuel mass injected altogether is also denoted as distributionfactor, and it influences the torque delivered by the internalcombustion machine.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve a method foroperating an internal combustion engine to the extent that the switchingfrom/to operating mode “HOSP” takes place in a manner that is astorque-neutral as possible, so that it is imperceptible to the driver ofa motor vehicle.

This object is attained, in a method of the present invention, of thekind mentioned at the outset, in that, during switching from/to thefirst operating mode “HOSP”, a distribution factor characterizing thefirst operating mode “HOSP” is taken into consideration in thecontroller.

Depending on the distribution factor selected, the torque of theinternal combustion engine in operating mode “HOSP” deviates up to 30%from the torque the internal combustion engine is able to deliver inhomogeneous operation, for example. Taking into account the dependenceof the torque on the distribution factor makes it possible to calculatea torque modification possibly occurring during switching over from/tooperating mode “HOSP”, for example, to/from homogeneous operation, evenbefore the time of the switching. Thereby it is possible, even beforethe switching, to calculate new injection parameters and the like, whichare set at the time of switching of the operating modes, so as to avoidthe torque modification mentioned.

It is of special advantage to undertake the consideration of thedistribution factor according to the present invention in an actualbranch and/or a setpoint branch of the controller of the internalcombustion engine, which minimizes the computing effort, since existingtorque models of the controller may be used, and an incorporation of thedistribution factor into the already present torque structure isparticularly simple to do.

One specific embodiment of the method according to the present inventionprovides that, in the actual branch of the controller, a torquereference variable is corrected using a distribution effectiveness thatis a function of the distribution factor. The actual branch of thecontroller is used, among other things, for calculating the actualmoment of the internal combustion engine, starting from the torquereference variable which is based on a reference state of the internalcombustion engine, which is characterized by a stoichiometric air/fuelmixture as well as an optimal ignition angle.

The correction of the torque reference variable according to the presentinvention adjusts the torque reference variable to the actual conditionsthat are frequently different from the reference state, so that,depending upon the distribution factor, a correct value for the actualmoment is supplied to the controller. One method variant according tothe present invention is also very advantageous, in which in thesetpoint branch of the controller a torque setpoint value is correctedusing the distribution efficiency that depends on the distributionfactor, so that for the further calculation of, for example, a fuelquantity to be injected as a function of the torque setpoint value,characteristics maps referring to the reference state may be used. Thedistribution efficiency is very expediently ascertained from acharacteristics curve/characteristics map.

Of special importance is the implementation of the method according tothe present invention in the form of a computer program which isprovided for a control unit of an internal combustion engine in a motorvehicle in particular. The computer program has program codes suitablefor carrying out the method according to the present invention, if it isexecuted on a computer. Furthermore, the program code may be stored on acomputer-readable data carrier, such as in a so-called flash memory. Inthis case, the present invention is thus implemented by the computerprogram, so that this computer program represents the present inventionin the same manner as the method, for the execution of which thecomputer program is suitable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of an exemplary embodiment of aninternal combustion engine according to the present invention.

FIG. 2 a shows a cutout from the actual branch of a controller.

FIG. 2 b shows a cutout from the setpoint branch of the controller ofFIG. 2 a.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 1 of a motor vehicle in whicha piston 2 is movable back and forth in a cylinder 3. Cylinder 3 isequipped with a combustion chamber 4, which, among other things, isdelimited by piston 2, an intake valve 5 and an exhaust valve 6. Anintake manifold 7 is connected to intake valve 5, and an exhaust pipe 8is connected to exhaust valve 6.

In the region of intake valve 5 and of discharge valve 6, a fuelinjector 9 and a spark plug 10 project into combustion chamber 4. Fuelis able to be injected into combustion chamber 4 via injector 9. Thefuel in combustion chamber 4 may be ignited by spark plug 10.

A rotatable throttle valve 11 through which air may be supplied tointake manifold 7 is accommodated in intake manifold 7. The quantity ofsupplied air is a function of the angle setting of throttle valve 11. Inexhaust pipe 8 a catalytic converter 12 is accommodated, which is usedfor cleaning the exhaust gases created by the combustion of the fuel.

From exhaust gas pipe 8, an exhaust gas recirculation pipe 13 goes backto intake manifold 7. In exhaust gas recirculation pipe 13 an exhaustgas recirculation valve 14 is accommodated, using which, the quantity ofthe exhaust gas recirculated into intake manifold may be set.

From a fuel tank 15, a tank ventilating line 16 leads to intake manifold7. In tank ventilating line 16 a tank ventilating valve 17 isaccommodated, using which the quantity of fuel vapor supplied to intakemanifold 7 from fuel tank 15 may be set.

Piston 2 is set into back and forth motion, by combustion of the fuel incombustion chamber 4, which is transmitted to a crank shaft (not shown)and exercises a torque upon it.

A control unit 18 receives input signals 19, which represent performancequantities of internal combustion engine 1 measured by sensors. Forinstance, control unit 18 is connected to an air mass sensor, a lambdasensor, an engine speed sensor or the like. Moreover, control unit 18 isconnected to an accelerator sensor which generates a signal thatindicates the setting of an accelerator operated by the driver, and thusgives the torque that is called for. Control unit 18 generates outputsignals 20, by which the performance of internal combustion engine 1 maybe influenced via actuators. For example, control device 18 is connectedto fuel injector 9, spark plug 10 and throttle valve 11 and the like,and generates the signals required for their control.

Among other things, control unit 18 is provided for controlling and/orregulating the performance quantities of internal combustion engine 1,which is symbolized by controller 21. For example, the fuel massinjected into combustion chamber 4 by fuel injector 9 is controlledand/or regulated by control unit 18 in particular with respect to lowfuel consumption and/or low pollutant generation. To this end, controlunit 18 is equipped with a microprocessor which has a program stored ina storage medium, particularly in a read-only memory, which is suitablefor execution of the control and/or regulation mentioned.

In a first operating mode, the so-called operating mode “HOSP”, a fuelmass to be injected into combustion chamber 4 is divided into twoindividual injections, of which the first takes place in the intakephase and the second in the compression phase of internal combustionengine 1. In this way, a rapid heating of catalytic converter 12 iseffected, which is important, for example, for a cold start of internalcombustion engine 1. The ratio of the fuel mass injected in the secondinjection to the total injected fuel mass is designated as thedistribution factor.

In an additional mode of operation, a so-called homogeneous operation ofinternal combustion engine 1, throttle valve 11 is partially opened orclosed as a function of the desired torque. The fuel is injected byinjector 9 into combustion chamber 4 during an intake phase caused bypiston 2. Turbulence is created in the injected fuel due to thesimultaneous air intake through throttle valve 11, and the fuel istherefore distributed in combustion chamber 4 in an essentially uniformmanner. Then the fuel/air mixture is compressed during the compressionphase and ignited by spark plug 10. The expansion of the ignited fueldrives piston 2. During homogeneous operation, the torque created is asubstantially a function of the position of throttle valve 11. From thestandpoint of low emissions, the fuel/air mixture is set as closely aspossible to lambda=1 or lambda<1.

Between the operating modes described of internal combustion engine 1,back and forth or reversed switching may occur. Such switchovers arecarried out by control unit 18. For example, after a cold start, thefirst operating mode, namely operating mode “HOSP”, may be set, by theuse of which catalytic converter 12 is rapidly heated to operatingtemperature. Depending on the distribution factor, the torque ofinternal combustion engine 1 is up to 30% less than in homogeneousoperation.

As soon as catalytic converter 12 has reached its operating temperature,control unit 18 switches internal combustion engine 1 over tohomogeneous operation. In order to achieve a switchover that istorque-neutral, the influence of the distribution factor on the torqueof internal combustion engine 1 in operating mode “HOSP” is taken intoconsideration in the manner explained below.

FIG. 2 a shows a cutout from the actual branch of controller 21, whichhas a torque reference value mioptl1 at its input end. This torquereference value miopt1 represents the maximum torque internal combustionengine 1 (FIG. 1) can deliver in response to stoichiometric air/fuelmixture, i.e. at lambda=1, and at an optimally set ignition angle.Torque reference value mioptl1 is ascertained, for example, on a teststand and serves as a reference value for all characteristiccurves/characteristics maps used in controller 21.

At the output end, the cutout shown in FIG. 2 a has actual moment mibas,which is calculated from torque reference value mioptl1.

Internal combustion engine 1 is not always operated at lambda=1 and theoptimal ignition angle, so that the actual available torque, actualmoment mibas, deviates from maximum possible torque reference valuemioptl1. This deviation is taken into account by computation incontroller 21.

To do so, torque reference value mioptl1 is first multiplied by a lambdaefficiency etalab1, which tells how the torque of internal combustionengine 1 changes as a function of lambda. In case lambda=1 applies, thelambda efficiency etalab1 turns out to have a value of 100%.Correspondingly, for a value of lambda

1, for which the torque of internal combustion engine 1 is, for example,only 80% of the torque reference value, a lambda efficiency of 80% comesabout.

Analogously to this, the dependence of the torque of internal combustionengine 1 on the distribution factor is taken into account in that theproduct of lambda efficiency etalab1 and torque reference value mioptl1is multiplied by a distribution efficiency etaaufte.

Distribution efficiency etaaufte, analogously to etalab1, gives thedependence of the torque on the distribution factor, and isadvantageously stored in the form of a characteristic curve in controlunit 18, preferably in rewritable memory, such as a flash memory.

Investigations have shown that distribution efficiency etaufte is also afunction of the rotational speed of internal combustion engine 1, sothat an especially accurate taking into account of the distributionfactor is possible with the aid of a characteristics map, which, besidesthe distribution factor, also contains the rotational speed.

Finally, there is a further multiplication step by ignition angleefficiency etazwbm. The resulting product represents actual momentmibas, which is processed further by controller 21 for thecontrol/regulation of internal combustion engine 1.

The formulation of the dependence of the torque on the variables lambda,distribution factor and ignition angle as efficiency is veryadvantageous, because thereby a multiplicative linkage of the variousinfluential factors is made possible. It is also possible, to multiplyall the efficiencies with one another, to obtain an overall efficiency.

FIG. 2 b shows a cutout from the setpoint branch of controller 21, atwhose input a driver command moment milsol, derived from an acceleratorsetting, is present. Driver command moment milsol is not related to thestate lambda=1, and is therefore prepared by computation for furtherprocessing in the setpoint branch of controller 21.

Setpoint torque misopl1 calculated back to lambda=1 is obtained,inversely to the calculation of actual moment mibas in the actualbranch, by successive division of driver command moment milsol by lambdaefficiency etalab1, distribution efficiency etaaufte and by ignitionangle efficiency etazwbm.

Setpoint torque misopli is supplied to a characteristics map KFMIRL,besides other variables such as the engine speed (not shown), whichgives the output value r1 of the cutout from the setpoint branch shownin FIG. 2 b.

Output value r1 is a measure for the setpoint value of the relative aircharge of combustion chamber 4, from which, at a given lambda, the fuelquantity to be injected may be ascertained.

The described inclusion of the distribution efficiency etaaufte in theactual and the setpoint branch of controller 21 makes possible atorque-neutral switchover from/to first operating mode “HOSP”, in thatthe torque which actually sets in is correctly calculated.

Besides the travel comfort, the method described also enormouslyincreases travel safety. Especially during switchover from firstoperating mode “HOSP” in homogeneous operation, in which internalcombustion engine 1 usually delivers a torque that is up to 30% greater,it is important to avoid a torque modification, in order to prevent asudden unintended acceleration of the motor vehicle.

Although first operating mode “HOSP” is usually set at cold start ofinternal combustion engine 1, it can happen that, even after a longeroperating time, switchover occurs once more, for example, fromhomogeneous operation to first operating mode “HOSP”, so that the takinginto account of distribution factor is of advantage even after a coldstart of internal combustion engine 1.

1. A method for operating an internal combustion engine, comprising: ina first operating mode, injecting a fuel into a combustion chamber; inthe first operating mode, dividing the fuel into two individualinjections, of which a first injection is injected in an intake phaseand a second injection is injected in a compression phase of theinternal combustion engine; injecting the fuel into the combustionchamber in at least one additional operating mode, wherein in the atleast one additional operating mode, the fuel is injected in the intakephase of the internal combustion engine; causing a controller to one ofcontrol and regulate the internal combustion engine; performing aswitchover between the first operating mode and the at least oneadditional operating mode, wherein in one of a switchover from the firstoperating mode and a switchover to the first operating mode, adistribution factor corresponding to the first operating mode is takeninto account in the controller, and wherein the distribution factorgives a ratio of injected fuel in the second injection to the totalinjected fuel; and in a setpoint branch of the controller, correcting atorque setpoint value using a distribution efficiency that is a functionof the distribution factor.
 2. The method as recited in claim 1,wherein: the fuel is injected into the combustion chamber in order toheat a catalytic converter.
 3. The method as recited in claim 1, furthercomprising: in an actual branch of the controller, correcting a torquereference value using the distribution efficiency.
 4. The method asrecited in claim 1, further comprising: ascertaining the distributionefficiency from a characteristics curve/characteristics map.
 5. Acomputer-readable storage medium for storing a computer program for acontrol unit of an internal combustion engine, the computer programhaving a program code that when executed results in a performance of thefollowing: in a first operating mode, injecting a fuel into a combustionchamber; in the first operating mode, dividing the fuel into twoindividual injections, of which a first injection is injected in anintake phase and a second injection is injected in a compression phaseof the internal combustion engine; injecting the fuel into thecombustion chamber in at least one additional operating mode, wherein inthe at least one additional operating mode, the fuel is injected in theintake phase of the internal combustion engine; causing a controller toone of control and regulate the internal combustion engine; performing aswitchover between the first operating mode and the at least oneadditional operating mode, wherein in one of a switchover from the firstoperating mode and a switchover to the first operating mode, adistribution factor corresponding to the first operating mode is takeninto account in controller, and wherein the distribution factor gives aratio of injected fuel in the second injection to the total injectedfuel; and in a setpoint branch of the controller, correcting a torquesetpoint value using a distribution efficiency that is a function of thedistribution factor.
 6. A control unit for operating an internalcombustion engine, comprising: an arrangement for, in a first operatingmode, injecting a fuel into a combustion chamber; an arrangement for, inthe first operating mode, dividing the fuel into two individualinjections, of which a first injection is injected in an intake phaseand a second injection is injected in a compression phase of theinternal combustion engine; an arrangement for injecting the fuel intothe combustion chamber in at least one additional operating mode,wherein in the at least one additional operating mode, the fuel isinjected in the intake phase of the internal combustion engine; anarrangement for causing a controller to one of control and regulate theinternal combustion engine; an arrangement for performing a switchoverbetween the first operating mode and the at least one additionaloperating mode, wherein in one of a switchover from the first operatingmode and a switchover to the first operating mode, a distribution factorcorresponding to the first operating mode is taken into account incontroller, and wherein the distribution factor gives a ratio ofinjected fuel in the second injection to the total injected fuel; and anarrangement for, in a setpoint branch of the controller, correcting atorque setpoint value using a distribution efficiency that is a functionof the distribution factor.
 7. An internal combustion engine,comprising: a control unit including: an arrangement for, in a firstoperating mode, injecting a fuel into a combustion chamber; anarrangement for, in the first operating mode, dividing the fuel into twoindividual injections, of which a first injection is injected in anintake phase and a second injection is injected in a compression phaseof the internal combustion engine; an arrangement for injecting the fuelinto the combustion chamber in at least one additional operating mode,wherein in the at least one additional operating mode, the fuel isinjected in the intake phase of the internal combustion engine; anarrangement for causing a controller to one of control and regulate theinternal combustion engine; an arrangement for performing a switchoverbetween the first operating mode and the at least one additionaloperating mode, wherein in one of a switchover from the first operatingmode and a switchover to the first operating mode, a distribution factorcorresponding to the first operating mode is taken into account incontroller, and wherein the distribution factor gives a ratio ofinjected fuel in the second injection to the total injected fuel; and anarrangement for, in a setpoint branch of the controller, correcting atorque setpoint value using a distribution efficiency that is a functionof the distribution factor.